In-pivot hybrid stepper motor for ball screw cam elevator mechanism for reduced-head hard disk drive

ABSTRACT

An approach to a reduced-head hard disk drive (HDD) involves an actuator elevator subsystem that includes a ball screw cam assembly with a hybrid permanent magnet (PM)-variable reluctance (VR) stepper motor disposed therein, to rotate the cam screw, which vertically translates an actuator arm assembly so that a corresponding pair of read-write heads can access different magnetic-recording disks of a multiple-disk stack. A suitably configured hybrid stepper motor can provide 200 full steps/rev for a 3.8 mm translation. Thus, to meet or surpass a step resolution of 6 μm/μstep or 0.5625°/μstep, the hybrid stepper motor would only need to be operated at 4 micro-step mode in order to achieve a 0.45°/μstep or 0.00475 mm/μstep, which enables a smoother motion since the available holding torque at the 4 th  micro-step provides sufficient torque margin to overcome load torque, frictional torque, and detent torque.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of and claims the benefit ofpriority to U.S. patent application Ser. No. 16/513,585, filed Jul. 16,2019, which claims the benefit of priority to U.S. Provisional PatentApplication No. 62/700,777, filed Jul. 19, 2018; to U.S. ProvisionalPatent Application No. 62/700,780, filed Jul. 19, 2018; to U.S.Provisional Patent Application No. 62/702,163, filed Jul. 23, 2018; toU.S. Provisional Patent Application No. 62/702,154, filed Jul. 23, 2018;and to U.S. Provisional Patent Application Ser. No. 62/747,623, filedOct. 18, 2018; the entire content of all of which is incorporated byreference for all purposes as if fully set forth herein.

FIELD OF EMBODIMENTS

Embodiments of the invention may relate generally to a reduced-head harddisk drive having an actuator elevator mechanism and particularly toapproaches to driving a low-profile ball screw cam actuator elevatormechanism.

BACKGROUND

There is an increasing need for archival storage. Tape is a traditionalsolution for data back-up, but is very slow to access data. Currentarchives are increasingly “active” archives, meaning some level ofcontinuing random read data access is required. Traditional hard diskdrives (HDDs) can be used but cost may be considered undesirably high.Other approaches considered may include HDDs with extra large diameterdisks and HDDs having an extra tall form factor, with both requiringlarge capital investment due to unique components and assemblyprocesses, low value proposition in the context of cost savings, andbarriers to adoption in the marketplace due to uniquely large formfactors, for example.

Any approaches described in this section are approaches that could bepursued, but not necessarily approaches that have been previouslyconceived or pursued. Therefore, unless otherwise indicated, it shouldnot be assumed that any of the approaches described in this sectionqualify as prior art merely by virtue of their inclusion in thissection.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated by way of example, and not by way oflimitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements and in which:

FIG. 1 is a plan view illustrating a hard disk drive, according to anembodiment;

FIG. 2A is a perspective view illustrating an actuator subsystem in areduced-head hard disk drive, according to an embodiment;

FIG. 2B is an isolated perspective view illustrating the actuatorsubsystem of FIG. 2A, according to an embodiment;

FIG. 2C is an isolated plan view illustrating the actuator subsystem ofFIG. 2A, according to an embodiment;

FIG. 3 is a cross-sectional side view illustrating an actuator elevatorassembly, according to an embodiment;

FIG. 4A is an exploded view illustrating a low-profile ball screw camassembly, according to an embodiment;

FIG. 4B is a partial cross-sectional view illustrating a portion of thecam assembly of FIG. 4A, according to an embodiment;

FIG. 4C is a partial cross-sectional view illustrating a portion of analternative cam assembly, according to an embodiment;

FIG. 5A is a perspective view illustrating an actuator-elevatorassembly, according to an embodiment;

FIG. 5B is a plan view illustrating the actuator-elevator assembly ofFIG. 5A, according to an embodiment;

FIG. 5C is a perspective view illustrating the actuator-elevatorassembly of FIG. 5A in a reduced-head data storage device, according toan embodiment;

FIG. 6A is an isolated perspective view illustrating an actuatorposition sensor and flexible cable assembly, according to an embodiment;

FIG. 6B is a perspective view illustrating the assembly of FIG. 6Aassembled with the actuator elevator assembly of FIG. 3, according to anembodiment;

FIG. 7A is a cross-sectional side view illustrating an actuator elevatorassembly with an in-pivot hybrid stepper motor, according to anembodiment;

FIG. 7B is a cross-sectional top view illustrating the actuator elevatorassembly and in-pivot hybrid stepper motor of FIG. 7A, according to anembodiment;

FIG. 8A is a top view illustrating a stator laminate for the in-pivothybrid stepper motor of FIG. 7A, according to an embodiment;

FIG. 8B is a perspective view illustrating the stator laminate assemblyfor the in-pivot hybrid stepper motor of FIG. 7A, according to anembodiment; and

FIG. 9 is a flow diagram illustrating a method for verticallytranslating a head-stack assembly (HSA) in a hard disk drive (HDD) toaccess multiple magnetic-recording disks, according to an embodiment.

DESCRIPTION

Approaches to a multi-disk hard disk drive having an actuator elevatormechanism are described. In the following description, for the purposesof explanation, numerous specific details are set forth in order toprovide a thorough understanding of the embodiments of the inventiondescribed herein. It will be apparent, however, that the embodiments ofthe invention described herein may be practiced without these specificdetails. In other instances, well-known structures and devices are shownin block diagram form in order to avoid unnecessarily obscuring theembodiments of the invention described herein.

Physical Description of an Illustrative Operating Context

Embodiments may be used in the context of a multi-disk, reducedread-write head, digital data storage device (DSD) such as a hard diskdrive (HDD). Thus, in accordance with an embodiment, a plan viewillustrating a conventional HDD 100 is shown in FIG. 1 to aid indescribing how a conventional HDD typically operates.

FIG. 1 illustrates the functional arrangement of components of the HDD100 including a slider 110 b that includes a magnetic read-write head110 a. Collectively, slider 110 b and head 110 a may be referred to as ahead slider. The HDD 100 includes at least one head gimbal assembly(HGA) 110 including the head slider, a lead suspension 110 c attached tothe head slider typically via a flexure, and a load beam 110 d attachedto the lead suspension 110 c. The HDD 100 also includes at least onerecording medium 120 rotatably mounted on a spindle 124 and a drivemotor (not visible) attached to the spindle 124 for rotating the medium120. The read-write head 110 a, which may also be referred to as atransducer, includes a write element and a read element for respectivelywriting and reading information stored on the medium 120 of the HDD 100.The medium 120 or a plurality of disk media may be affixed to thespindle 124 with a disk clamp 128.

The HDD 100 further includes an arm 132 attached to the HGA 110, acarriage 134, a voice-coil motor (VCM) that includes an armature 136including a voice coil 140 attached to the carriage 134 and a stator 144including a voice-coil magnet (not visible). The armature 136 of the VCMis attached to the carriage 134 and is configured to move the arm 132and the HGA 110 to access portions of the medium 120, all collectivelymounted on a pivot shaft 148 with an interposed pivot bearing assembly152. In the case of an HDD having multiple disks, the carriage 134 maybe referred to as an “E-block,” or comb, because the carriage isarranged to carry a ganged array of arms that gives it the appearance ofa comb.

An assembly comprising a head gimbal assembly (e.g., HGA 110) includinga flexure to which the head slider is coupled, an actuator arm (e.g.,arm 132) and/or load beam to which the flexure is coupled, and anactuator (e.g., the VCM) to which the actuator arm is coupled, may becollectively referred to as a head stack assembly (HSA). An HSA may,however, include more or fewer components than those described. Forexample, an HSA may refer to an assembly that further includeselectrical interconnection components. Generally, an HSA is the assemblyconfigured to move the head slider to access portions of the medium 120for read and write operations.

With further reference to FIG. 1, electrical signals (e.g., current tothe voice coil 140 of the VCM) comprising a write signal to and a readsignal from the head 110 a, are transmitted by a flexible cable assembly(FCA) 156 (or “flex cable”). Interconnection between the flex cable 156and the head 110 a may include an arm-electronics (AE) module 160, whichmay have an on-board pre-amplifier for the read signal, as well as otherread-channel and write-channel electronic components. The AE module 160may be attached to the carriage 134 as shown. The flex cable 156 may becoupled to an electrical-connector block 164, which provides electricalcommunication, in some configurations, through an electricalfeed-through provided by an HDD housing 168. The HDD housing 168 (or“enclosure base” or “baseplate” or simply “base”), in conjunction withan HDD cover, provides a semi-sealed (or hermetically sealed, in someconfigurations) protective enclosure for the information storagecomponents of the HDD 100.

Other electronic components, including a disk controller and servoelectronics including a digital-signal processor (DSP), provideelectrical signals to the drive motor, the voice coil 140 of the VCM andthe head 110 a of the HGA 110. The electrical signal provided to thedrive motor enables the drive motor to spin providing a torque to thespindle 124 which is in turn transmitted to the medium 120 that isaffixed to the spindle 124. As a result, the medium 120 spins in adirection 172. The spinning medium 120 creates a cushion of air thatacts as an air-bearing on which the air-bearing surface (ABS) of theslider 110 b rides so that the slider 110 b flies above the surface ofthe medium 120 without making contact with a thin magnetic-recordinglayer in which information is recorded. Similarly in an HDD in which alighter-than-air gas is utilized, such as helium for a non-limitingexample, the spinning medium 120 creates a cushion of gas that acts as agas or fluid bearing on which the slider 110 b rides.

The electrical signal provided to the voice coil 140 of the VCM enablesthe head 110 a of the HGA 110 to access a track 176 on which informationis recorded. Thus, the armature 136 of the VCM swings through an arc180, which enables the head 110 a of the HGA 110 to access varioustracks on the medium 120. Information is stored on the medium 120 in aplurality of radially nested tracks arranged in sectors on the medium120, such as sector 184. Correspondingly, each track is composed of aplurality of sectored track portions (or “track sector”) such assectored track portion 188. Each sectored track portion 188 may includerecorded information, and a header containing error correction codeinformation and a servo-burst-signal pattern, such as anABCD-servo-burst-signal pattern, which is information that identifiesthe track 176. In accessing the track 176, the read element of the head110 a of the HGA 110 reads the servo-burst-signal pattern, whichprovides a position-error-signal (PES) to the servo electronics, whichcontrols the electrical signal provided to the voice coil 140 of theVCM, thereby enabling the head 110 a to follow the track 176. Uponfinding the track 176 and identifying a particular sectored trackportion 188, the head 110 a either reads information from the track 176or writes information to the track 176 depending on instructionsreceived by the disk controller from an external agent, for example, amicroprocessor of a computer system.

An HDD's electronic architecture comprises numerous electroniccomponents for performing their respective functions for operation of anHDD, such as a hard disk controller (“HDC”), an interface controller, anarm electronics module, a data channel, a motor driver, a servoprocessor, buffer memory, etc. Two or more of such components may becombined on a single integrated circuit board referred to as a “systemon a chip” (“SOC”). Several, if not all, of such electronic componentsare typically arranged on a printed circuit board that is coupled to thebottom side of an HDD, such as to HDD housing 168.

References herein to a hard disk drive, such as HDD 100 illustrated anddescribed in reference to FIG. 1, may encompass an information storagedevice that is at times referred to as a “hybrid drive”. A hybrid driverefers generally to a storage device having functionality of both atraditional HDD (see, e.g., HDD 100) combined with solid-state storagedevice (SSD) using non-volatile memory, such as flash or othersolid-state (e.g., integrated circuits) memory, which is electricallyerasable and programmable. As operation, management and control of thedifferent types of storage media typically differ, the solid-stateportion of a hybrid drive may include its own corresponding controllerfunctionality, which may be integrated into a single controller alongwith the HDD functionality. A hybrid drive may be architected andconfigured to operate and to utilize the solid-state portion in a numberof ways, such as, for non-limiting examples, by using the solid-statememory as cache memory, for storing frequently-accessed data, forstoring I/O intensive data, and the like. Further, a hybrid drive may bearchitected and configured essentially as two storage devices in asingle enclosure, i.e., a traditional HDD and an SSD, with either one ormultiple interfaces for host connection.

Introduction

References herein to “an embodiment”, “one embodiment”, and the like,are intended to mean that the particular feature, structure, orcharacteristic being described is included in at least one embodiment ofthe invention. However, instance of such phrases do not necessarily allrefer to the same embodiment,

The term “substantially” will be understood to describe a feature thatis largely or nearly structured, configured, dimensioned, etc., but withwhich manufacturing tolerances and the like may in practice result in asituation in which the structure, configuration, dimension, etc. is notalways or necessarily precisely as stated. For example, describing astructure as “substantially vertical” would assign that term its plainmeaning, such that the sidewall is vertical for all practical purposesbut may not be precisely at 90 degrees.

While terms such as “optimal”, “optimize”, “minimal”, “minimize”, andthe like may not have certain values associated therewith, if such termsare used herein the intent is that one of ordinary skill in the artwould understand such terms to include affecting a value, parameter,metric, and the like in a beneficial direction consistent with thetotality of this disclosure. For example, describing a value ofsomething as “minimal” does not require that the value actually be equalto some theoretical minimum (e.g., zero), but should be understood in apractical sense in that a corresponding goal would be to move the valuein a beneficial direction toward a theoretical minimum.

Recall that there is an increasing need for cost effective “active”archival storage (also referred to as “cold storage”), preferably havinga conventional form factor and utilizing many standard components. Oneapproach involves a standard HDD form factor (e.g., a 3.5″ form factor)and largely common HDD architecture, with a non-zero finite number of ndisks in one rotating disk stack, but containing fewer than 2nread-write heads, according to embodiments. Such a storage device mayutilize an articulation mechanism that can move the heads to mate withthe different disk surfaces (for a non-limiting example, only 2 headsbut 5+ disks for an air drive or 8+ disks for a He drive), where theprimary cost savings may come from eliminating the vast majority of theheads in the drive.

For a cold storage data storage device, a very thin structure (e.g., theread-write head stack assembly, or “HSA”) needs to be moved whilekeeping perpendicular to the axis on which it is moving. That structurealso needs to maintain sufficient stiffness for structural and resonancecontrol. There may be ball screws on the market that may comply withsuch requirements, but they are taller than the shaft they ride on andare typically considerably expensive.

With other possible approaches, there is a concern that when theactuator arms are unlocked during the time they need to be moved up anddown to get to different disks, the interface between the arms and thecam rattles or is relatively loose. This could cause undesirable motionin the suspensions and heads as the arms are raised and lowered. Thereis also a large range of potential friction between the cam threads, armthreads, and lock nut threads that could over time cause extra wear andbad repeatability in the vertical positioning achieved.

Actuator Subsystem for Reduced-Head Hard Disk Drive

FIG. 2A is a perspective view illustrating an actuator subsystem in areduced-head hard disk drive (HDD), FIG. 2B is an isolated perspectiveview illustrating the actuator subsystem of FIG. 2A, and FIG. 2C is anisolated plan view illustrating the actuator subsystem of FIG. 2A, allaccording to embodiments. FIGS. 2A-2C collectively illustrate anactuator subsystem comprising a low profile ball screw cam assembly 202(or “cam 202”), which transforms rotary motion into linear motion, witha stepper motor 204 (or “stepping motor”) disposed therein to form anactuator elevator subassembly, which is disposed within the actuatorpivot and pivot bearing of the actuator subsystem (e.g., the “pivotcartridge”) and is configured to vertically translate at least oneactuator arm 205 (see, e.g., arm 132 of FIG. 1) along with a respectiveHGA 207 (see, e.g., HGA 110 of FIG. 1). According to an embodiment, theactuator subsystem for a reduced-head HDD consists of two actuator arm205 assemblies each with a corresponding HGA 207 (e.g., a modified HSA,in which the actuator arm assemblies translate vertically, or elevate,while the VCM coil 209 may be fixed in the vertical direction) housing acorresponding read-write head 207 a (see, e.g., read-write head 110 a ofFIG. 1). Generally, the term “reduced-head HDD” is used to refer to anHDD in which the number of read-write heads is less than the number ofmagnetic-recording disk media surfaces.

With respect to electrical signal transmission, FIGS. 2A-2C furtherillustrate a flexible cable assembly 208 (“FCA 208”), which isconfigured to comprise a dynamic vertical “loop” 208 a (“FCA verticalloop 208 a”) for vertical translation of the end(s) that are coupled tothe actuator elevator subassembly and/or another portion of the actuatorsubsystem. This FCA vertical loop 208 a is in addition to a typicaldynamic horizontal loop for horizontal translation purposes for when theactuator to which one end is connected is rotating. The actuatorsubsystem further comprises at least one connector housing 210 forhousing an electrical connector for transferring electrical signals(e.g., motor power, sensor signals, etc.) between the actuator elevatorsubassembly and a ramp elevator assembly (described in more detailelsewhere herein).

With respect to actuator arm locking, FIGS. 2A-2C further illustrate anarm lock subsystem 206, coupled with or constituent to a coil supportassembly 212, configured to mechanically interact with an outer diametercrash stop 211 (“ODCS 211”) to lock and unlock the actuator elevatorsubassembly, as described in more detail elsewhere herein.

Actuator Elevator Assembly

FIG. 3 is a cross-sectional side view illustrating an actuator elevatorassembly, according to an embodiment. The actuator elevator assembly 300illustrated in FIG. 3 is configured for use in an actuator subsystem asillustrated and described in reference to FIGS. 2A-2C, i.e., configuredto vertically translate at least one actuator arm 205 (shown here is aportion of the arm 205 that engages with the pivot; see, e.g., FIGS.2A-2C, 4A-4C) with a respective HGA 207 (FIGS. 2B, 2C) and read-writehead 207 a (FIGS. 2B, 2C).

Actuator elevator assembly 300 comprises the actuator elevatorsubassembly comprising the ball screw cam 202, having the stepper motor204 coupled to (e.g., with an outer sleeve adhered to the inner surfaceof the cam 202) and disposed therein and interposed between the cam 202and a pivot shaft 310, where the pivot shaft 310 bottom is shownpositioned within an opening of a bottom support plate 308 b and thepivot shaft 310 top is shown positioned approaching or within an openingof a top support plate 308 a. In a typical HDD configuration, the innerpivot shaft 310 is further coupled to an HDD enclosure base (see, e.g.,housing 168 of FIG. 1) via a screw or other fastener and to an HDD cover(not shown) via another screw or fastener, effectively sandwiching thepivot shaft 310 and the actuator elevator assembly 300 more broadlywithin the corresponding HDD.

Actuator elevator assembly 300 further comprises a first set or pair ofHSA pivot bearings 302 (along with upper inner bearing housing 302 a andlower inner bearing housing 302 b) interposed between the pivot shaft310 and the stepper motor 204 (e.g., one bearing assembly near the topand one bearing assembly near the bottom). HSA pivot bearings 302function to support loads associated at least in part with the rotationof the actuator arms 205 (FIGS. 2A-2C), along with the stepper motor 204and the cam 202 to which it is attached, about the stationary pivotshaft 310, such as during actuator seek/read/write/load/unloadoperations. Actuator elevator assembly 300 further comprises a secondset or pair of cam bearings 304 interposed between the stepper motor 204and the cam 202 (e.g., one bearing assembly near the top and one bearingassembly near the bottom). Cam bearings 304 function to support loadsassociated at least in part with the rotation of the stepper motor 204and the cam 202 about the stationary pivot shaft 310 (when the actuatorelevator subassembly is decoupled from the HSA pivot inner bearinghousing 302 a, 302 b, as described in more detail elsewhere herein withrespect to the operation of the arm lock subsystem 206), such as duringactuator vertical translation operations.

Actuator elevator assembly 300 further comprises a third set of ballscrew bearings comprising balls 202 c and retainer 202 b interposedbetween a cam screw 202 a (see, e.g., FIGS. 4A-4C) and the actuator arm205. This ball screw bearing assembly functions to support loadsassociated at least in part with the rotation of the stepper motor 204and the cam 202 about the stationary pivot shaft 310 and the consequentactuator vertical translation operations.

Low Profile Ball Screw Cam

According to an embodiment, one approach to an actuator elevatormechanism for a cold storage HDD uses a multi-start threaded shaft (alsoreferred to as a “multi-start ball screw”) with a ball in each start tocreate a plane perpendicular to the screw/cam. The balls are heldequally spaced around the shaft by a bearing retainer. The balls arepreloaded to the shaft at all times by compressing the two outer races.This platform is stable and does not rattle or function loosely, thusproviding consistent structural integrity.

FIG. 4A is an exploded view illustrating a low-profile ball screw camassembly, and FIG. 4B is a partial cross-sectional view illustrating aportion of the cam assembly of FIG. 4A, according to an embodiment. Theillustrated ball screw cam assembly referred to as cam 202 comprises thehollow threaded shaft or screw 202 a, a bearing retainer 202 b orretaining ring with a plurality of equally-spaced retained balls 202 c,a bearing half-race 202 d, an O-ring 202 e, and, optionally, a C-clip202 f, according to an embodiment. Cam 202 is configured for use in theactuator elevator assembly 300 illustrated in FIG. 3, which isconfigured for use in the actuator subsystem illustrated and describedin reference to FIGS. 2A-2C, i.e., to vertically translate at least oneactuator arm 205 with a respective HGA 207 and read-write head 207 a.However, use of a cam mechanism such as cam 202 in implementationsoutside of such an actuator subsystem (e.g., in a camera, or in otherproducts requiring a miniature cam/translation mechanism) iscontemplated, so the use scenarios for cam 202 are not limited toimplementations only within such an actuator subsystem.

It is noteworthy that with cam 202, according to an embodiment, thenumber of starts equals the number of balls, thereby providing a stableplanar “platform” with a single bearing assembly and perpendicular tothe axis/translation path. According to an embodiment, three balls 202 care held within the bearing retainer 202 b, thereby providing a 3-pointplanar bearing assembly while facilitating the low-profile aspect of thecam 202. While three balls are needed to define or construct the plane,the number of balls 202 c may vary from implementation toimplementation. While greater than three balls 202 c provides a morestable planar platform (e.g., more contact points about the shaftprovides more actuator arm stiffness and stability), a greater number ofballs 202 c would also increase the thread pitch and lead correspondingto the screw thread (especially in view of a stepper motor driver),perhaps undesirably in some use scenarios.

With reference to FIG. 4B, one can see that the tapered starts/threadsof screw 202 a function as upper and lower portions of an inner race ofthe bearing assembly of cam 202. According to an embodiment, the outerrace of the bearing assembly of cam 202 is a split-race, i.e., a 2-partrace (whereby the two outer load surfaces are split among two parts),comprising a tapered inner surface 205 a of the opening in arm 205 as alower outer race surface, and a tapered lower surface of bearinghalf-race 202 d as an upper outer race surface, together forming whatmay be referred to as a v-notch outer race. The bearing assembly istherefore preloaded radially at four points of contact via the inner andouter races, while the O-ring 202 e (e.g., elastomeric) functions as aspring to provide a variable compression force applied to the bearinghalf-race 202 d, in conjunction with the C-clip 202 f Alternatively touse of an elastomeric O-ring 202 e (e.g., which can degrade and causecreep over time), according to an embodiment a wavy washer, functioningas a metallic spring, may be implemented to provide the compressionforce to the outer race. Hence, this arrangement functions to manage orcompensate for the possibility of slight changes in the diameter of theinner race/threads at various locations along the length of the screw202 a, such as those associated with part tolerances and manufacturingvariability.

Furthermore, one could eliminate use of the C-clip 202 f and reconfigurethe outer race, as illustrated in FIG. 4C. FIG. 4C is a partialcross-sectional view illustrating a portion of an alternative camassembly, according to an embodiment. As with the embodiment illustratedin FIG. 4B, the tapered starts/threads of screw 202 a function as upperand lower portions of an inner race of the bearing assembly of thisembodiment of ball screw cam, cam 203. Here also the outer race of thebearing assembly of cam 203 is a split-race, or 2-part race, comprisinga tapered half-race 202 d-1 as a lower outer race surface and a taperedhalf-race 202 d-2 as an upper outer race surface (bonded to an innersurface of the opening in arm 205 after preloading), together formingwhat may be referred to as a v-notch outer race. Here also the bearingassembly is therefore preloaded radially at four points of contact viathe inner and outer races, while the O-ring 202 e (or wavy washer)functions as a spring to provide a variable compression force applied tothe bearing split-race comprising 202 d-1, 201 d-2.

In-Pivot Claw-Pole Stepper Motor

In the context of a cold storage HDD that includes a rotary cam (e.g.,cam 202) that is rotated with respect to the coil assembly (e.g., VCMcoil 209), which would vertically move the actuator arms 205 up and downfrom disk to disk, a means to provide that rotation is needed. Accordingto an embodiment and with reference to FIGS. 2A-3, a stepper motor 204is assembled within the pivot (or, the pivot cartridge) of the actuatorsubsystem (FIGS. 2A-2C), which, in conjunction with the cam 202 (FIGS.4A-4B), forms an actuator elevator assembly 300 (FIG. 3).

So-called “claw-pole” designs contain an inner permanent magnet (PM)mounted on a rotary lead-screw shaft. In the context of a multi-disk HDDhaving an actuator elevator mechanism, the actuator subsystem designcomprises a stationary shaft during the translation of the head stackassembly (HSA) to switch between magnetic recording disks. With this, aunique design of a claw-pole stepper motor is needed. The smaller magnetvolume of a typical claw-pole motor where the stator circumscribes thePM requires a high number of turns (100 or more) with a very smallcopper wire (e.g. 0.05 millimeter (mm)) due to the physical limitations.Because electromagnetic torque, T_(e)=kD²L, is proportional to thesquare of the diameter of the magnetic air gap and the stator stacklength, it is advantageous to maximize the motor diameter.

However, winding with a smaller wire diameter is difficult due to itsfragility and is more susceptible to the fluctuation of the windingtension that causes wider distribution of the winding resistance. A highnumber of turns with a small diameter wire results in a higher copperloss, P_(copper loss)=i²R, and subsequent heat that may adversely affectthe internal environment of the HDD in terms of the dynamic read-writehead gap due to potential ball-bearing oil migration. Thus, in theconfined space of the cold storage data storage device rotary cam, it ispreferable to implement a compact stepper motor to rotate the cam inorder to move the HSA bi-directionally in the vertical direction toaccess different disks in the stack.

A claw-pole motor such as stepper motor 204 comprises, for example, twouni-filar windings in injection-molded-plastic spools for bipolarcontrol and four claw-pole stators made from cold-rolled steel sheetmetal, electrical steel sheet metal, SMC (Soft Magnetic Composite), andthe like, where use of electrical steel with various levels of siliconcontent or SMC reduces the eddy current loss. Furthermore, use of SMCcan produce a complex geometry through powder metallurgy, unlike stampedand formed electrical steel sheet. Each stator contains p/2 teeth(p=number of poles) (e.g., 5 teeth per claw-pole stator according to anembodiment of stepper motor 204 having a 10-pole PM). The step angle ofa stepper motor depends on the number of poles and stator teeth. In adesign having 10 poles and 20 teeth, suitable for the intended purpose,the step angle/rotation is 18° or 20 steps/revolution in a full-stepcontrol, with both stator assemblies having a pair of claw-pole statorsshifted relative to the other by one-half pole width, and where the stepangle is inversely proportional to the number of stator teeth. Likewise,a design with 100 teeth yields 360°/100 or 3.6°/step angle, for example.In the case of 4 start-threaded rotary cam, this 3.6° step angle wouldprovide 4 mm/100 steps or 0.04 mm step resolution rather than 4 mm/20steps or 0.2 mm step resolution, thus providing a more precise andaccurate servo control for positioning the HSA between the disks. Statedotherwise, a higher number of the claw (stator) teeth provides for asmaller step resolution. However, the outer diameter (OD) of the system(e.g., cam 202) limits the possible number of claw teeth. That is, witha given OD there is a practical limit to the number of teeth implementedbecause adding more teeth reduces their size and leads to manufacturingdifficulty, magnetic saturation, and unstable tooth structures. Forexample, with an 18 mm OD, the system could be limited to 40 teeth and astep angle of 360°/40 or 9°. To get a higher step resolution, amicro-step may be used, where a typical bi-polar driver provides ½, ¼,⅛, 1/16, and 1/32 micro-steps.

A corresponding rotor of stepper motor 204 comprises a PM (e.g. Nd—Fe—B)attached to the inner diameter of the cam 202 (see, e.g., FIG. 3),which, according to an embodiment, is constructed of ferritic stainlesssteel, and where the PM comprises 10 hetero-polar magnets. Hence, whenthe coils are energized the teeth become north and south poles, andmutual torque is established when the north PM poles align with thesouth claw poles and the south PM poles align with the north claw poles.Reversing the current polarity in the stator coils reverses the polarityof the electromagnetic claw poles and the resultant torque advances therotor one full step.

Note that the number of coils and corresponding claw-pole stator pairs(i.e., phases), and the number of corresponding teeth on each claw-polestator, may vary from implementation to implementation based on specificdesign goals (e.g., torque, phases and rotational degrees/step orsteps/revolution) and, therefore, are not limited by the numberdescribed in the foregoing example. For example, with a 2-inchform-factor HDD, a four-coil design is feasible, which equates to 9°step angle, i.e., 360°/(number of teeth per claw)*(number ofclaws)=360°/(4*10)=9°/step. Alternatively, the step angle can becomputed from the corresponding number of rotor poles and phases, i.e.,360°/(2 phases*20 rotor poles)=9°/step.

With reference back to FIG. 3, stepper motor 204 comprises a circular“phase A” coil 320 a (with or without corresponding bobbin) enveloped bya pair of corresponding circular and mating claw-poles stators 321 a, acircular “phase B” coil 320 b (with or without corresponding bobbin)enveloped by a pair of corresponding circular and mating claw-polestators 321 b, disposed within a circular permanent magnet 322 (“PM322”), all positioned around the stationary shaft 310. Note that whenthe HSA moves (e.g., actuator arm 205 seeks), the cam 202 and the HSApivot bearing 302 upper and lower housing 302 a, 302 b movesynchronously and thus eliminate the differential reluctance or coggingtorque that must be overcome in the rotary motion of the HSA.

According to an embodiment, it is noteworthy that in-pivot stepper motor204 is configured with an outer rotor and inner stators. That is, incontrast with typical stepper motors, here the PM 322 is on the outsideof the stepper motor 204 assembly and the claw-poles 321 a, 321 b andcoils 320 a, 320 b are on the inside of the PM 322. Likewise, while aconventional stepper motor typically rotates a central shaft, here theshaft 310 is fixed/stationary and the PM 322 rotor is bonded to theinner diameter of the cam shaft or screw 202 a such that the steppermotor 204 rotates the outer cam 202 about the fixed inner shaft 310. Inthat sense, this embodiment of stepper motor 204 is akin to aconventional stepper motor that is “turned inside-out”.

Method of Assembling an Actuator Elevator Subassembly

A method of assembling an actuator elevator subassembly, according to anembodiment, is as follows. The described method may be used to assemblean assembly comprising the cam 202 and a 10-pole stepper motor such asin-pivot stepper motor 204, for example. However, as described elsewhereherein, the number of poles may vary from implementation toimplementation and therefore, is not so limited.

First, insert the upper HSA pivot bearing 302 into the upper innerbearing housing 302 a and bond (e.g., glue) the outer race of the upperHSA pivot bearing 302 to the upper inner bearing housing 302 a. Next,insert the upper cam bearing 304 around the inner bearing housing 302 aand bond the inner race of the upper cam bearing 304 to the upper innerbearing housing 302 a. Once these bearings 302, 304 are assembled, themethod moves on to the stepper motor 204, as follows.

Insert around, orient, and bond a claw-pole stator 321 a (a first halfof a first pair) to an outer sleeve portion of the upper inner bearinghousing 302 a. Next, insert within and bond a first coil 320 a to thefirst claw-pole stator 321 a of the first pair. Next, rotate a claw-polestator 321 a (the second half of the first pair) 36° relative to thefirst claw-pole stator 321 a of the first pair and bond the second halfof the claw-pole stator 321 a to the outer sleeve portion of the upperinner bearing housing 302 a. Next, rotate a claw-pole stator 321 b (afirst half of a second pair) 18° relative to the second claw-pole stator321 a of the first pair and bond the first half of the claw-pole stator321 b of the second pair to the outer sleeve portion of the upper innerbearing housing 302 a. Next, insert around and bond a second coil 320 bto the upper inner bearing housing 302 a. Next, rotate a claw-polestator 321 b (the second half of the second pair) 36° relative to thefirst claw-pole stator 321 b of the second pair and bond the second halfof the claw-pole stator 321 b to the outer sleeve portion of the upperinner bearing housing 302 a. Insert a magnetized PM 322 (magnetized toproduce 10 pole, or 5 pole-pairs) and bond the outer diameter surface ofthe PM 322 to in the inner diameter surface of the screw 202 a. Once thestepper motor is assembled as above, the method moves on to the lowerbearings, as follows.

Insert the lower HSA pivot bearing 302 into the lower inner bearinghousing 302 b and bond the outer race of the lower HSA pivot bearing 302to the lower inner bearing housing 302 b. Next, insert the lower cambearing 304 around the lower inner bearing housing 302 b and bond theinner race of the lower cam bearing 304 to the lower inner bearinghousing 302 b. Next, bond the outer race of the lower cam bearing 304,now in assembly form with the lower HSA pivot bearing 302 and the lowerinner bearing housing 302 b, into the screw 202 a subassembly. Next,apply bonding adhesive completely around the outer diameter periphery ofthe upper inner bearing housing 302 a, and apply bonding adhesive to theouter race of the upper cam bearing 304, and insert this subassemblyinto the screw 202 a subassembly. Next, apply an adhesive bead to thelower inner bearing housing 302 b and insert that lower bearing assemblyinto the screw 202 a subassembly and the upper bearing subassembly.Finally, heat-cure the thermoset adhesive by placement of the assemblyin an oven, for example.

Locking/Unlocking Mechanism for Vertically Translatable ActuatorAssembly

FIG. 5A is a perspective view illustrating an actuator-elevatorassembly, FIG. 5B is a plan view illustrating the actuator-elevatorassembly of FIG. 5A, and FIG. 5C is a perspective view illustrating theactuator-elevator assembly of FIG. 5A in a reduced-head data storagedevice, all according to an embodiment. According to an embodiment andwith reference to FIGS. 2A-4B, the locking/unlocking mechanism isconstituent to the actuator subsystem (FIGS. 2A-2C) and which operatesto vertically lock the actuator arm in place during seek/read/writeoperations, for example, and to unlock the actuator arm for verticaltranslation under the control of the cam 202 (FIGS. 4A-4B) and thestepper motor 204 (FIGS. 2A-3) constituent to the actuator elevatorassembly 300 (FIG. 3).

FIGS. 5A-5C collectively illustrate a locking/unlocking mechanismpreviously-introduced as arm lock subsystem 206 (hereinafter, “lockingmechanism 206”), located in the general area labeled as B-B in FIG. 5A.Locking mechanism 206 comprises a tab 206 d extending from actuator arm205 into a slot 206 e within the structure of coil support assembly 212,whereby the tab 206 d is squeezed, held, locked within the slot 206 ewhen in a cam locked position and is released, unlocked from thecompression of the slot 206 e and therefore free to travel in thevertical direction when in a cam unlocked position. According to anembodiment, the tab 206 d and/or the clamping surfaces of the slot 206 eare coated with a low-wear, high-coefficient of friction material toprovide for strong clamping while inhibiting the undesirable particlegeneration within the drive. Locking mechanism 206 further comprises aspring mechanism 206 b disposed within a slit 206 c within the coilsupport assembly 212, wherein the slit 206 c intersects the slot 206 e.According to an embodiment, the spring mechanism 206 b is a sheet-likepiece of material that is relatively thin, and long in the verticaldirection in comparison with its width positioned coincident within theslit 206 c. The spring mechanism 206 b is rigid enough andconfigured/positioned within the slit 206 c spanning across the slot 206e such that the force produced by the spring mechanism 206 b, in alocked or default position (i.e., slightly bent along a vertical axis toelicit a spring-like force), compresses each side of the slot 206 etoward each other to squeeze and hold the tab 206 d in a fixed positionwithin the slot 206 e.

The cam is unlocked when the force associated with the spring mechanism206 b is overcome, thereby opening wider the slot 206 e, such that thetab 206 d is released from the hold of the slot 206 e and therebyenabled to travel vertically within the slot 206 e so that the actuatorarm 205 from which the tab 206 d extends can be vertically translated bythe actuator elevator assembly 300. The force of spring mechanism 206 bis overcome when a lock arm 206 a, which is part of or constituent tothe coil support assembly 212, and which is part of or extension of oneside of the slot 206 e, mechanically interacts with thepreviously-introduced ODCS 211, according to an embodiment.Alternatively, interaction with a mechanical element, feature, orstructure other than a crash stop could be used to overcome the holdingforce of the spring mechanism 206 b. As such, when the actuator arm 205is driven/rotated far enough past the outer diameter of the disk stack,the lock arm 206 a “crashes” into the ODCS 211, which causes the lockarm 206 a to rotate (e.g., counter-clockwise) which then functions toopen the gap corresponding to slot 206 e (e.g., similarly to how aclothes-pin functions).

Flexible Cable Assembly with Vertical Loop

FIG. 6A is an isolated perspective view illustrating an actuatorposition sensor and flexible cable assembly, and FIG. 6B is aperspective view illustrating the assembly of FIG. 6A assembled with theactuator elevator assembly of FIG. 3, both according to an embodiment.According to an embodiment and with reference to FIGS. 2A-5C, theillustrated actuator position sensor and flexible cable assembly areconstituent to the actuator subsystem (FIGS. 2A-2C), which provides forvertical translation of the actuator arm 205 under the control of thecam 202 (FIGS. 4A-4B) and the stepper motor 204 (FIGS. 2A-3) constituentto the actuator elevator assembly 300 (FIG. 3).

Conventional HDDs typically include a flexible cable assembly (FCA) suchas FCA 156 of FIG. 1, which require some slack in the horizontaldirection (e.g., XY direction) to allow for the distance between itsconnection points to vary in the horizontal direction in response toactuator rotation, as one connection point is with part of the actuatorarm. However, an FCA cable for a rotating and vertically translatingactuator connects to an actuator that not only moves in the XY plane forseeking data on the disk, but also moves in the Z direction to moveamong the disks in the multi-disk stack. Thus, a complete flex may bedesigned as either a one part solution or designed as two differentparts combined together, with the use of a connector to carry electricalsignals. With an actuator that is configured to move vertically, such asin the context of the actuator subsystem described in reference to ofFIGS. 2A-5C, according to an embodiment the FCA 208 (see, e.g., FIGS.2A-2C, not shown here), which moves in the XY direction such as duringseeking, further comprises or is electronically coupled or spliced witha dynamic vertical loop portion of FCA, referred to as FCA vertical loop208 a, which moves effectively independently of the FCA 208 portion suchas when the actuator is vertically translating. Functionally similar tothe FCA 156, the FCA vertical loop 208 a provides some slack in the Zdirection to allow for the distance between its connection points tovary in the vertical direction in response to actuator verticaltranslation, as one connection point is with part of the actuator arm205. Both the horizontal loop of FCA 208 and the FCA vertical loop 208 aare configured to move independently of the other.

Note that the configuration and shape of the FCA vertical loop 208 a mayvary from implementation to implementation. According to an embodiment,a “U-loop” configuration is implemented for FCA vertical loop 208 a (theloop generally resembles a letter “U” in various not-fully-extendedstates), as depicted in FIGS. 6A-6B. However, other shaped verticalloops may be designed and implemented for use in this context, such as aC-loop shape that resembles the letter “C” when not fully extended andan S-loop shape that resembles the letter “S” when not fully extended,and the like. In the configuration depicted, the FCA vertical loop 208 ais positioned near a preamp 606 and whereby the XY loop of FCA 208electrically connects the FCA vertical loop 208 a to a bracket and/or aconnector housing 210 (see, e.g., FIGS. 2A-2C).

Further illustrated in FIGS. 6A-6B is a pair of proximity or positionsensors 602 coupled to the actuator arm 205 and configured to sense theZ position of the actuator arm 205 (e.g., vertical height) relative to amagnetic encoding strip and, ultimately, relative to the disk stack.According to an embodiment, one or more Hall effect sensors mounted in aquadrature configuration are implemented for the position sensor(s) 602,which function in coordination with a closely-positioned magneticencoder strip 604, mounted on a stiffener 605, to provide sine andcosine signals for sensing the directions and crossing of the waveforms.The stiffener 605 may further function for positioning of the FCA 208and FCA vertical loop 208 a.

Generally, magnetic flux density in the air gap between the Hall sensorsand the permanent magnet scale (i.e., magnetic encoding strip 604)should be set at an optimum gap range to provide adequate signalstrength. A narrow gap causes signal saturation and a wide gap weakensthe signal. In either case, detection of the zero-crossing points isuncertain. However, the quadrature configuration of the Hall sensors inconjunction with a 1 mm pole-pitch magnetic scale provides displacementand direction simultaneous by virtue of the leading and lagging natureof the waveforms in the upward and downward translations. For example,one Hall sensor signal leads when the stepper motor moves downward, andanother Hall sensor signal leads when the stepper motor moves upward. Aleading Hall sensor signal indicates the translational direction and thezero-crossing points of the sine-cosine waveforms provide the amount ofthe displacement.

In-Pivot Hybrid Stepper Motor

In the context of a cold storage HDD that includes a rotary cam (e.g.,cam 202 of FIGS. 2A-5C) that is rotated with respect to an actuator coilassembly (e.g., VCM coil 209 of FIGS. 2B, 2C, 5A, 5B), which wouldvertically move a head-stack assembly (HSA) comprising one or moreactuator arms (e.g., actuator arm 205 of FIGS. 2A-2C, 4A-4C, 5A, 5B) upand down from disk to disk, a means to provide that rotation is needed.According to an embodiment and with reference to FIGS. 2A-2C, a hybridstepper motor 704 is assembled within the pivot (or, the pivotcartridge) of the actuator subsystem (FIGS. 2A-2C), which, inconjunction with a cam such as the cam 202 (FIGS. 4A-4B), forms anactuator elevator assembly similar to actuator elevator assembly 300(FIG. 3), however with the hybrid stepper motor 704 substituted for aclaw-pole stepper motor embodying stepper motor 204.

In the context of a multi-disk HDD having an actuator elevatormechanism, the actuator subsystem design comprises a stationary shaftduring the translation of the head stack assembly (HSA) to switchbetween magnetic recording disks. Furthermore, in the confined space ofthe cold storage data storage device rotary cam, it is preferable toimplement a compact stepper motor to rotate the cam in order to move theHSA bi-directionally in the vertical direction to access different disksin the stack. With this, a unique design of a stepper motor is needed.

The holding torque of a stepper motor reduces precipitously in themicro-stepping mode. For a 40 full steps/rev claw-pole stepper motor toprovide the required step resolution to place the read-write heads ontothe disk surfaces, it must be driven in a 16 micro-step (μstep) mode. Inthis case, the holding torque may not always supply enough margin toovercome the variation in the load torque, frictional torque, and detenttorque. Consequently, missteps happen often. However, the currentmanufacturing capability of the progressive dies can only mass-produce a32 full steps/rev claw pole motor. In this case, the 16 μstep resolutionbecomes worse and the holding torque in μstep mode still has inadequatemargin to overcome the variation of the frictional torque, load torqueand the detent torque. Consequently, the μstep displacement profile maydeviate from the desirable linearity.

A hybrid permanent magnet (PM)-variable reluctance (VR) stepper motor(or simply “hybrid stepper motor”) as described herein can overcome theforegoing issues and provide, for a non-limiting example, 200 fullsteps/rev for a 3.8 mm translation. Consequently, to meet or surpass thedesired step resolution (for a non-limiting example, 6 μm/μstep), a1.8°/full-step hybrid stepper motor would only need to be operated at 4micro-steps to surpass the minimum vertical displacement of 0.006mm/μstep, which enables a smoother motion since the available holdingtorque at the 4^(th) micro-step provides significantly adequate torquemargin to overcome the load torque, frictional torque, and detenttorque.

FIG. 7A is a cross-sectional side view illustrating an actuator elevatorassembly with an in-pivot hybrid stepper motor, and FIG. 7B is across-sectional top view illustrating the actuator elevator assembly andin-pivot hybrid stepper motor of FIG. 7A, both according to embodiments.Actuator elevator assembly 700 comprises a permanent magnet(PM)-variable reluctance (VR) hybrid stepper motor 704 (or simply“hybrid stepper motor 704”). A hybrid stepper motor refers to acombination of aspects of variable reluctance and permanent magnet typemotors, wherein the rotor is axially magnetized, meaning one end ismagnetized as a north pole and the other end a south pole, like apermanent magnet stepper motor, and the stator is electromagneticallyenergized like a variable reluctance stepper motor. Hybrid stepper motor704 comprises an outer rotor assembly 706 (“rotor 706”) and an innerstator assembly 708 (“stator 708”) disposed within the rotor 706, whichcooperatively provide an axial magnetic flux path. Hybrid stepper motor704 is depicted installed around a central pivot shaft 710, e.g.,functionally similar to the inner pivot shaft 310 of FIG. 3, and withina low profile ball screw cam assembly 702 (or “cam 702”) comprising ascrew 702 a, e.g., functionally similar to the cam 202 of FIGS. 2A-3and, according to an embodiment, structurally similar to the cam 202 andassociated sub-components of FIGS. 4A-4C. Furthermore, cam 702 may beimplemented in an assembly as depicted in FIGS. 5A-5C. Thus, the cam 702and the hybrid stepper motor 704 may be substituted for the cam 202 andthe stepper motor 204 in each of the aspects and embodiments of cam 202and stepper motor 204 as described throughout herein. For a non-limitingexample, the hybrid stepper motor 704 may be implemented similarly to(e.g., substituted for functionally and operationally) the stepper motor204 of FIG. 3.

As with the cam 202, cam 702 transforms rotary motion into linearmotion, with the stepper motor 704 (or “stepping motor”) disposedtherein to form an actuator elevator subassembly, which is disposedwithin the actuator pivot and pivot bearing of the actuator subsystem(e.g., the “pivot cartridge”) and is configured to vertically translateat least one actuator arm 205 (see, e.g., arm 132 of FIG. 1) along witha respective HGA 207 (see, e.g., HGA 110 of FIG. 1). As such, theactuator elevator assembly 300 of FIG. 3 may comprise the actuatorelevator subassembly comprising the ball screw cam 702, having thehybrid stepper motor 704 coupled to (e.g., with an outer sleeve adheredto the inner surface of the cam 702) and disposed therein and interposedbetween the cam 702 and the pivot shaft 710. As with a typical HDDconfiguration, the pivot shaft 710 may be further coupled to an HDDenclosure base (see, e.g., housing 168 of FIG. 1) via a threaded lowerend (as depicted in FIG. 7A) or a screw or other fastener, and to an HDDcover via another screw or fastener, effectively sandwiching the pivotshaft 710 and the actuator elevator assembly 300 more broadly within thecorresponding HDD.

According to an embodiment, the outer rotor 706 comprises a plurality ofsingle-pole-axially-magnetized PM rings 712 (for a non-limiting example,5 pieces×1.5 mm thick) stacked alternatively between stacks oflaminations 714 (or “lam stacks 714”) (for a non-limiting example, 4stacks of 24×0.2 mm electrical steel laminations). According to anembodiment, Nd—Fe—B (e.g. Daido NP-12L 50 kOes) permanent magnets may beutilized for the PM rings 712. According to an embodiment found suitablefor the intended purpose (see, e.g., FIGS. 8A, 8B), the inner stator 708is 23 mm long, with either 115×0.2 mm (electrical steel) laminations or230×0.1 mm (electrical steel) laminations, which may vary fromimplementation to implementation based on design goals, constraints,etc.

According to an embodiment, it is noteworthy that in-pivot hybridstepper motor 704 is configured with an outer rotor and inner stator.That is, in contrast with typical stepper motors, here the PMs 712 arepositioned at the outside of the hybrid stepper motor 704 assembly andthe stator 708 and corresponding coils 718 are positioned inside of thePMs 712. Likewise, while a conventional stepper motor typically rotatesa central shaft, here the shaft 710 is fixed/stationary and the rotor706 is bonded to the inner diameter of the cam screw 702 a such that thestepper motor 704 rotates the outer cam 702 about the fixed inner shaft710. In that sense, this embodiment of hybrid stepper motor 204 is akinto a conventional stepper motor that is “turned inside-out”.

FIG. 8A is a top view illustrating a stator laminate for the in-pivothybrid stepper motor of FIG. 7A, and FIG. 8B is a perspective viewillustrating the stator laminate assembly for the in-pivot hybridstepper motor of FIG. 7A, both according to embodiments. According to anembodiment, the stator 708 comprises eight (8) main poles 716 with eachpole comprising five (5) teeth 717, which is found to be suitable forthe intended purpose. Hybrid stepper motor 704 further comprises aplurality of coils 718 (not shown here for purposes of clarity; see FIG.7B) wound on each of the main poles 716 of the stator 708 to form phasesA and B. For example, and with reference to FIG. 7B, pole 1 isconfigured for phase A (South), pole 2 is configured for phase B(North), pole 3 is configured for phase A (North), pole 4 is configuredfor phase B (South), and so on.

According to an embodiment, each of the lam stacks 714 of the rotor 706comprises fifty (50) inner diameter (ID) teeth 720 having a 7.2° toothpitch as shown in FIG. 7B. Two lam stacks 714 are assembled so that itsteeth are shifted by one-half (½) tooth pitch angle, or 3.6°. Together,the teeth 720 of the two sets of the rotor 706 lam stacks 714 mutuallyinteract with the teeth 717 on the stator 708 to step 1.8°/full step,based on the midpoint of a tooth 717 on the stator 708 to the midpointon the nearest tooth 720 on the rotor 706 (i.e., 200 full steps/rev).When the phases A and B are energized, the stator 708 teeth 717 and therotor 706 teeth 720 become north and south poles. Mutual torque isestablished due to the attraction between the north rotor poles and thesouth stator poles. Likewise, the south rotor poles attract the northstator poles. Reversing the current polarity in the stator 708 coils 718reverses the polarity of the main poles 716 and the resultant torqueadvances the rotor 706 one full step. According to an embodiment and asdepicted in FIG. 7A, to increase torque two additional (beyond thetypical two) sets of lam stacks 714 are implemented for a total of four(4) lam stacks 714 for the rotor 706.

Actuator elevator assembly 700 further comprises a first set or pair ofcam bearings 701 (e.g., one bearing assembly near the top and onebearing assembly near the bottom) to support loads associated at leastin part with the rotation of the stepper motor 704 and the cam 702 aboutthe stationary pivot shaft 710, such as during actuator verticaltranslation operations. Actuator elevator assembly 700 further comprisesa second set or pair of HSA pivot bearings 703 (e.g., one bearingassembly near the top and one bearing assembly near the bottom) tosupport loads associated at least in part with the rotation of theactuator arms 205 (FIGS. 2A-2C), along with the hybrid stepper motor 704and the cam 702 to which it is attached, about the stationary pivotshaft 710, such as during actuator seek, read, write, load, unloadoperations. That is, when the cam 702 is locked with the VCM-actuator,the entire assembly behaves like a traditional rotary VCMA(Voice-Coil-Motor Assembly) where the HSA rotates around the pivot shaft710 via the pivot bearings 703.

A hybrid stepper motor configured as described herein can provide 200full steps/rev for a 3.8 mm translation. Thus, to meet or surpass a stepresolution of 6 μm/μstep or 0.5265°/μstep (i.e., 360°/40 full steps/16μsteps), the hybrid stepper motor would only need to be operated at 4micro-step mode in order to achieve a 0.45°/μstep (i.e., 360°/200 fullsteps/4 μsteps) or 0.00475 mm/μstep (i.e., 3.8 mm/200 full steps/4μsteps) (as opposed to that of the 40 full steps/rev of the claw-polemotor operated in 16 μsteps (i.e., 9°/16=0.5625°/μstep or 0.0059mm/μstep)), which enables a smoother motion since the available holdingtorque at the 4th micro-step provides sufficient torque margin toovercome load torque, frictional torque, and detent torque.

Method for Translating a Head-Stack Assembly to Access Multiple Disks

FIG. 9 is a flow diagram illustrating a method for verticallytranslating a head-stack assembly (HSA) in a hard disk drive (HDD) toaccess multiple magnetic-recording disks, according to an embodiment.FIG. 9 is described in further reference to components illustrated inFIGS. 7A-8B and, as discussed elsewhere herein, hybrid stepper motor 704may be installed within and operate in conjunction with cam 702, e.g.,functionally similar to the cam 202 of FIGS. 2A-3 and structurallysimilar to the cam 202 and associated sub-components of FIGS. 4A-4C, andmay be implemented in an assembly as depicted in FIGS. 5A-5C. That is,the hybrid stepper motor 704 may be implemented similarly to (e.g.,substituted for functionally and operationally) the stepper motor 204 ofFIG. 3 and the corresponding applications, implementations, andinstallations described in reference thereto.

At block 902, a permanent magnet (PM)-variable reluctance (VR) hybridstepper motor that is disposed within a ball screw cam assemblycomprising a screw is driven, to rotate the screw about a coaxial (e.g.,with the hybrid stepper motor) shaft. For example, hybrid stepper motor704 disposed with cam 702 is driven, e.g., by applying electricalcurrent to the hybrid stepper motor 704, thereby rotating the screw 702a of the cam 702.

At block 904, a planar multi-ball bearing assembly, which is coupledwith a hard disk drive (HDD) head-stack assembly (HSA) is allowed totranslate (e.g., vertically) in response to rotation of the screw. Forexample, driving the rotation of the screw 702 a via the hybrid steppermotor 704 drives translation of an HSA comprising one or more actuatorarms (e.g., actuator arm 205 of FIGS. 2A-2C, 4A-4C, 5A, 5B, coupled withthe bearing balls 202 c and retainer 202 b of FIGS. 4A-4C) up and downfrom disk to disk along the length of screw 702 a. Thus, the read-writehead(s) of the HSA is enabled to access and perform read operations andwrite operations on each respective magnetic recording disk (e.g., diskmedium 120) of a multi-disk stack of a reduced-head HDD.

According to an embodiment, translation of the HSA includes translating(e.g., vertically) a multi-ball bearing assembly coupled with the HSA,by each of a particular number of balls of the bearing assembly ridingin a corresponding respective start of the same particular number ofstarts of the multi-start screw. For example, translation of the HSAincludes translating (e.g., vertically) actuator arms (e.g., similar toactuator arm 205 of FIG. 4A) coupled with the HSA, by each of aparticular number of balls (e.g., similar to balls 202 c of FIGS. 4A-4C)of the bearing assembly riding in a corresponding respective start orthread of the same particular number of starts of the multi-start screw702 a (e.g., similar to screw 202 a of FIGS. 4A-4C). Thus, as describedin reference to FIGS. 4A-4C, with the number of starts equaling thenumber of balls a stable planar “platform” is provided with a singlebearing assembly perpendicular to the axis/translation path.

At block 906, while the bearing assembly is translating, the verticalposition of the HSA is sensed. For example, as illustrated in FIGS.6A-6B a pair of proximity or position sensors 602 may be coupled to theactuator arm 205 and configured to sense the Z position of the actuatorarm 205 (e.g., vertical height) relative to a magnetic encoding stripand, ultimately, relative to the disk stack.

EXTENSIONS AND ALTERNATIVES

In the foregoing description, embodiments of the invention have beendescribed with reference to numerous specific details that may vary fromimplementation to implementation. Therefore, various modifications andchanges may be made thereto without departing from the broader spiritand scope of the embodiments. Thus, the sole and exclusive indicator ofwhat is the invention, and is intended by the applicants to be theinvention, is the set of claims that issue from this application, in thespecific form in which such claims issue, including any subsequentcorrection. Any definitions expressly set forth herein for termscontained in such claims shall govern the meaning of such terms as usedin the claims. Hence, no limitation, element, property, feature,advantage or attribute that is not expressly recited in a claim shouldlimit the scope of such claim in any way. The specification and drawingsare, accordingly, to be regarded in an illustrative rather than arestrictive sense.

In addition, in this description certain process steps may be set forthin a particular order, and alphabetic and alphanumeric labels may beused to identify certain steps. Unless specifically stated in thedescription, embodiments are not necessarily limited to any particularorder of carrying out such steps. In particular, the labels are usedmerely for convenient identification of steps, and are not intended tospecify or require a particular order of carrying out such steps.

What is claimed is:
 1. An actuator system for a reduced-head hard diskdrive (HDD), the system comprising: a ball screw cam assembly; ahead-stack assembly (HSA) translatably coupled with the cam assembly; apermanent magnet (PM)-variable reluctance (VR) hybrid stepper motordisposed within and affixed to a screw of the cam assembly, andconfigured to drive rotation of the screw to drive translation of theHSA along an axis of the screw; and a fixed shaft around which thestepper motor is positioned; wherein the hybrid stepper motor isrotatable about the fixed shaft to drive the rotation of the screw, thehybrid stepper motor comprising: a plurality of ring-shaped permanentmagnets (PMs), a stack of electrical steel lamination rings interposedbetween each adjacent pair of the PMs, wherein the PMs and thelamination rings are affixed to an inner diameter of the screw andcollectively operate as a rotor of the hybrid stepper motor, a stator,disposed within the rotor, comprising a stack of electrical steellaminations configured with a plurality of main poles each having aplurality of teeth, and a coil wound on each of the main poles.
 2. Theactuator system of claim 1, wherein: the plurality of ring-shaped PMscomprises at least three PMs in a stacked formation; and the pluralityof lamination rings comprises a stack of lamination rings between eachof the at least three PMs.
 3. The actuator system of claim 1, whereinthe hybrid stepper motor further comprises: five (5) PMs, of theplurality of PMs, disposed in a stacked formation; and four (4) stacksof lamination rings, of the plurality of lamination rings, with onestack positioned between each of the adjacent PMs; wherein the five PMsare all unidirectionally axially magnetized.
 4. The actuator system ofclaim 1, wherein the stator consists of eight (8) main poles, with eachmain pole consisting of five (5) teeth.
 5. The actuator system of claim4, wherein each of the lamination rings of the rotor consists of fifty(50) teeth.
 6. The actuator system of claim 5, wherein at least onestack of the lamination rings is assembled one-half (½) tooth pitchoffset from another stack of the lamination rings.
 7. A hard disk drivecomprising the actuator system of claim
 6. 8. The actuator system ofclaim 1, wherein the cam assembly and the disposed hybrid stepper motorare configured as an actuator pivot cartridge in the HDD.
 9. Theactuator system of claim 1, wherein the ball screw cam assemblycomprises: a hollow screw comprising at least three starts, a ballbearing assembly comprising a same number of balls as starts, whereineach ball rides in a corresponding start, thereby forming a plane onwhich the balls ride perpendicular to the axis of the screw.
 10. Theactuator system of claim 1, further comprising: one or more proximitysensors coupled with the HSA; and a magnetic encoder strip positioned inclose proximity to the one or more proximity sensors, and configured toprovide a magnetic field for sensing by the one or more proximitysensors.
 11. A hard disk drive comprising the actuator system of claim10.
 12. A hard disk drive comprising the actuator system of claim
 1. 13.A permanent magnet (PM)-variable reluctance (VR) hybrid stepper motorconfigured to rotate about a fixed shaft, the hybrid stepper motorcomprising: a plurality of ring-shaped permanent magnets (PMs); a stackof electrical steel lamination rings interposed between each adjacentpair of the PMs; wherein the PMs and the lamination rings are affixed toan inner diameter of the screw and collectively operate as a rotor ofthe hybrid stepper motor; a stator, disposed within the rotor,comprising a stack of electrical steel laminations configured with aplurality of main poles each having a plurality of teeth; and a coilwound on each of the main poles.
 14. The permanent magnet (PM)-variablereluctance (VR) hybrid stepper motor of claim 13, further comprising:five (5) PMs, of the plurality of PMs, disposed in a stacked formation;and four (4) stacks of lamination rings, of the plurality of laminationrings, with one stack positioned between each of the adjacent PMs;wherein the five PMs are all unidirectionally axially magnetized. 15.The permanent magnet (PM)-variable reluctance (VR) hybrid stepper motorof claim 13, wherein the stator consists of eight (8) main poles, witheach main pole consisting of five (5) teeth.
 16. The permanent magnet(PM)-variable reluctance (VR) hybrid stepper motor of claim 15, whereineach of the lamination rings of the rotor consists of fifty (50) teeth.17. The permanent magnet (PM)-variable reluctance (VR) hybrid steppermotor of claim 16, wherein at least one stack of the lamination rings isassembled one-half (½) tooth pitch offset from another stack of thelamination rings.
 18. A hard disk drive (HDD) head-stack assembly (HSA)pivot assembly comprising the PM-VR hybrid stepper motor of claim 13disposed within a ball screw cam assembly and configured to driverotation of the cam assembly to drive vertical translation of the HSA.19. A method for vertically translating a head-stack assembly (HSA) in ahard disk drive (HDD) to access multiple magnetic-recording disks, themethod comprising: driving a permanent magnet (PM)-variable reluctance(VR) hybrid stepper motor disposed within a ball screw cam assemblycomprising a screw, thereby rotating the screw about a coaxial fixedshaft; allowing a planar multi-ball bearing assembly that is coupledwith the HSA to translate vertically in response to rotating the screw;and while the bearing assembly is translating, sensing the verticalposition of the HSA.
 20. A reduced-head hard disk drive (HDD),comprising: recording means for storing digital information;reading/writing means for reading from and writing to the recordingmeans; means for moving the reading/writing means to access portions ofthe recording means; a permanent magnet (PM)-variable reluctance (VR)hybrid stepper motor rotating means for rotating cam means about a fixedshaft for translating the reading/writing means from one recording meansto another recording means; and means for sensing a vertical position ofthe reading/writing means.